Developments in technology have been accompanied by an increased reliance on fuel sources, and such fuel sources are becoming increasingly limited and difficult to acquire. With the burning of fossil fuels taking place at an unprecedented rate, it is likely that the world's fuel demand will soon outweigh the current fuel supplies.
The majority of fuel sources currently produced are from petroleum sources or from the chemical processing of vegetable oils. Petroleum sources face a number of problems: they are non-renewable resources, they require an extensive period of time (years) to form, and formation is restricted to distinct locations. As petroleum is consumed as a source of energy, geological petroleum resources eventually will be depleted.
As a result, efforts have been directed toward harnessing sources of renewable energy, such as sunlight, water, wind, and biomass. The use of biomasses to produce new sources of fuel which are not derived from petroleum sources (i.e., biofuel) has emerged as one alternative option. Biofuel (e.g., biodiesel) is a biodegradable combustible fuel made of long chain alkanes and esters. Biodiesel can be used in most internal combustion diesel engines in either a pure form, which is referred to as “neat” biodiesel, or as a mixture in any concentration with regular petroleum diesel.
In theory, biofuel can be produced from any biological carbon source. The most common biological carbon source, by far, is photosynthetic plants that capture solar energy. Many different plants and plant-derived materials are used to manufacture biofuels. One of the greatest technical challenges is to develop ways to convert biomass energy specifically to liquid fuels for transportation. A commonly used strategy to produce biofuel is to grow sugar crops (e.g., sugar cane or sugar beet) or starch crops (e.g., corn or maize) and then use yeast fermentation to produce ethanol (i.e., ethyl alcohol). Another commonly used strategy to produce biofuel is to grow plants that naturally produce oils, such as oil palm, soybean, or jatropha. An alternative source of naturally produced oil is from organisms, such as algae. When these oils are heated, their viscosity is reduced, and they can be burned directly in a diesel engine. Alternatively, the oils can be chemically processed to produce fuels, such as biodiesel. Current methods of making biodiesel involve transesterification of triacylglycerides (e.g., vegetable oil or animal fat) which leads to a mixture of fatty esters and the unwanted side product glycerin. This results in a product that is heterogeneous and a waste product that leads to economic inefficiencies.
Vegetable oils remain an attractive alternative to fossil fuels because they are renewable resources. However, vegetable oils are an important part of the food chain. It is unlikely that sufficient crops can be grown to meet the needs for both food and industrial chemicals, such as fuels and polymers. In addition, oil-producing plants can be restricted by the environmental conditions in which they flourish. Furthermore, vegetable oils are not hydrocarbons (e.g., alkanes or alkenes). Rather, vegetable oils are primarily triglycerides, which contain oxygen molecules, that when burned in a combustion engine will coke up the engine.
In view of the foregoing, it would be desirable to enable the production of fuels from alternative sources in order to provide an improved method of producing biofuels. The invention provides nucleic acid sequences that encode polypeptides that are involved in the biosynthesis of hydrocarbons and hydrocarbon intermediates. In addition, the invention provides methods of using the same for the production of biofuels. The invention described herein overcomes the problems associated with limited, non-renewable hydrocarbon resources and provides improved methods that can be used to produce biofuels. These and other advantages of the invention will become apparent from the detailed description provided herein.